This invention relates to an imaging apparatus in which the dynamic range can be substantially increased even with the use of a solid image sensor, such as a CCD image sensor.
An imaging apparatus (imager) is in extensive use in a video tape recorder (VTR) with a built-in camera or as a video camera unit of a still video camera. As an imager for this video camera unit, a solid-state image sensor, such as a CCD image sensor, has come into widespread use.
As compared to, for example, a silver salt photographic system, the solid state image sensor has a narrow dynamic range. Thus, during imaging in backlight, a reproduced picture exhibits an extremely high or low luminance level.
In such case, it has been customary with the conventional imager to adjust the diaphragm for achieving an optimum light exposure volume for a main object. However, if only the diaphragm is adjusted, so-called white-skip is produced in the background, even if an optimum reproduced picture corresponding to the main object is obtained, such that the background picture is a of plain white color due to the white skip.
Thus it has been customary to compress the level of an output for the standard light to a range within approximately 1.0 V.sub.p-p by knee processing, as shown in FIG. 1. That is, if, with the conventional imager employing the solid-state image sensor, the incident light volume indicated on the abscissa in FIG. 1 is increased, the picture output level shown on the ordinate is increased linearly, such that an output beyond the range of approximately 1.0 V.sub.p-p is produced and hence the output picture is of a plain white color. Thus, knee processing is performed as indicated in FIG. 1 by way of level compression. That is, the dynamic range with respect to the incident light is increased by compressing the output level with respect to the incident light. The picture signal, thus level-compressed by the knee processing, has a maximum of four-fold to five-fold dynamic range with respect to the standard light.
Recently, a high-quality picture has been desired in the field of a video camera, and a broader dynamic range is needed, such that dynamic range expansion by level compression of the output exceeding the standard light by the above-mentioned knee processing is felt to be insufficient.
On the other hand, the usage of special effect pictures is also increased, such that facilitated control of the level compression is desired.